The invention is directed to a method of cleaning and/or drying the inner walls of projected pipelines, wherein the vapour formed by evaporation of the substance adhering to the pipe inner wall and, if applicable, present foreign gases are exhausted from the pipeline by means of one or several exhausting apparatus.
A method of this type has been known from the DE-OS No. 2,950,542. In the known method, the medium exhausted from the pipeline is directly introduced into the exhausting apparatus. The exhausting apparatus used is a system of single or multi-stage sucking jet nozzles comprising, for instance, a plurality of nozzles disposed in series so that successively higher vacuum stages can be obtained. Multi-plate vacuum pumps are mentioned as a further suitable exhausting apparatus for vacuum-type drying of pipelines. Insofar as said publication also mentions interstage condensors, experience has shown that condensors are concerned which are provided downstream of the first stage of a multi-stage vacuum plant and at which--due to the already effected partial compression--the water vapour heated to about 60.degree. to 100.degree. C. is condensed on cooling surfaces maintained at a temperature of from 20.degree. to 30.degree. C. so that the succeeding vacuum stages are protected from the effects of water vapour.
The drying rate of the known vacuum-type drying process is determined solely by the suction capacity of the vacuum system. The latter cannot be increased as desired, because with increasing vacuum also the pressure losses in the usual pipe unions provided on a pig trap will increase.
It is the object of the instant invention to considerably increase the drying rate of a vacuum-type drying method of the known type by the use of simple means.